[Nek5000-users] weak derivative, dssum and binvm1 in cvode_driver

[nek5000-users at lists.mcs.anl.gov]

Hi Emmanuel

>From what I recall:
CVODE solves the governing non-linear eqns in the strong form. That¹s why we
have to project every term of the RHS onto H2 (dssum and collocate with
bintm1). The sum is projected again onto H2 because it gets devided by
vtrans. Hope this helps.

Cheers,
Stefan

Von:  <nek5000-users at lists.mcs.anl.gov>
Antworten an:  <nek5000-users at lists.mcs.anl.gov>
Datum:  Thursday, June 5, 2014 at 9:20 AM
An:  "nek5000-users at lists.mcs.anl.gov" <nek5000-users at lists.mcs.anl.gov>
Betreff:  Re: [Nek5000-users] weak derivative, dssum and binvm1 in
cvode_driver

I¹m adding another quick question:

why in the routine makeq, under the cvode statement, there are these
following 2 lines:
             call col2(bq,bintm1,ntot)
             call col2(bq,bm1,ntot)

I¹m not sure to understand why we are multiplying bq by the inverse of the
mass matrix (bintm1) and just after multiplying it back by the mass matrix
(bm1). Moreover, after leaving the makeq routine, fctfun will multiplying
again ydot=bq/vtrans by the inverse of the mass matrix.

Why all of these operations? Thank you for your help !



Best regards,
Emmanuel



On 5 Jun 2014, at 12:14, <nek5000-users at lists.mcs.anl.gov>
<nek5000-users at lists.mcs.anl.gov> wrote:

> Dear Nek team, 
> 
> I have a quick question: in cvode_driver.f, in the routine fcvfun, do all the
> derivatives must be in weak formulation (using wgradm1) when constructing the
> right hand side term ydot?
> Because at the end of the routine fcvfun,  dssum and multiplication by binvm1
> are applied to the right hand side term ydot.
> 
> It¹s also not clear to me if I need to apply dssum and binvm1 for each
> derivative term appearing in my equation (in other terms, each time after
> calling wgradm1), or if I need to apply dssum and binvm1 only to the whole RHS
> term ydot ?
> 
> I¹m afraid of inconsistency if apply twice dssum and binvm1: one during the
> construction of operators and one on the final ydot term.
> 
> Thank you for you help !
> 
> Best regards,
> Emmanuel
> 
> 
> 
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